Iron County register. [volume] (Ironton, Iron County, Mo.) 1867-1965, 1887-08-25
ToRNADoEs AND CYCLONES.


The Difference I'm the Formation Of Tor
nado-whirls and whirlwinds.
When the conditions of atmospheric
instability have given birth to tor.
nado, the fact is announced to the oh.
server by a sudden gathering of dark.
swift-whirling clouds, from which de
pend writhing. serpent-like body
formed of condensed vapor This
writhing column extends rapidly
downward until it touches the earth.
When it attains the surface it becomes
audible from the violent rending &C
tons which it creates upon that sur
face. As soon as the whirl is created
it begins to move away-generally
toward the northeastern the evident
reason that the upper cold layer OF air
against which it originates has. in the
northern hemisphere, movement in
that direction In its path over the
surface the circling movement of the
writing air and the sucking action OF
the partial vacuum in the central por-
ton of the shaft combine to bring
about an extreme devastation. On
the outside of the whirl the air. which
rushes in circling path toward the
vortex, overturns all movable objects,
and in the center these objects. if not
too heavy, are sucked up as by a great
air-pump. Thus the roofs of
houses-bodies of men and animals
may be lifted to great elevations. until
they are tossed by the tumultuous move
ments beyond the limits of the ascend
ing currents and fall upon the earth.
Where the center of the whirlwind
passes over a building the sudden de-
crease in the pressure of the outer air
often causes the atmosphere which is
contained within the walls suddenly
to press against the sides of the struct-
ure, SO that these sides are quickly
driven outward as If by charge of
gunpowder. 1t is not unlikely that
the dimunition of pressure brought
about by the passage of the interior of
the whirl over building may be about
as much as is indicated by the fall of
four inches in the barometer. This is
equivalent to a change in the pressure
amounting to about three hundred
pounds to the square foot This force
operates to burst out the walls OF a
building. 1t is not improbable thst
the diminution of pressure may be
much greater than this, but even the
amount named is sufficient to account
for the bursting out of the frail-walled
structures which these devastating
movements encounter in the western
parts of the United States
The way in which these tornado
whirls are formed differs in certain es-
sential particulars from the way in
which whlrlwinds are created. as has
been well shown by Prof. FerreL The
most important points of difference are
as follows: The dust-whirls are due to
the heating of thin layer of air next
the ground. The small mass OF this
layer prevents its upward whirling
from bringing about any powerful
movements of the atmosphere. In the
tornado the heat of the lower air has
different origin. When a cyclone
passes over the surface of the country.
certain peculiar movements of the at
mosphere which it produces bring
large volumes of the warm and moist
ened air to the earth's surface and
overlap them by cool stratum. This
layer of warm, moist air tends to rise
up for the same reason that the thin
layer of dry air which forms the dust
whirl is impeled upward. but on ac-
count of its great mass the intensity of
the upward urgence is far greater. In
the sand-whirl the upward motion be-
gins close to the earth's surface, for
the reason that the stratum which is
impeled upward is very thin, but in
the tornado the stratum of heated
air is usually about a thousand
feet thick; therefore its whirling
action naturally originates at the up
per surface of the hot layer. for it is at
that point the upward motion begins
Starting in this upper region, the whirl
extends progressively downward. just
as in the bath-tub the whirl extends
progressively upward from the point
at which the motion originated. until
the wind may touch the surface of the
earth When these whirls begin they
only involve a small part of the air
about the point of origin, and so the
acquired velocity of the particles when
they come to the center is not great;
but gradually they suck air from far
Their and farther away. As the field of
supply becomes larger, and the par
ticles move from a greater distance,
they approach that center with greater
speed, and the spiral widens and turns
with accelerated velocity.
Fortunately the paths of tornadoes
are ordinarily very narrow-the wild
est have a diameter of less than two
miles; the narrowest of only forty feet
In most cases a tornado is seriously
over width not exceed
ing five hundred feet The length
Of the tornado's path across
The country does not commonly exceed
thirty miles, and it generally traverses
he distance in about ap hour. When
the upward corkscrew motion of the
outer part of the spiral aud the swifter
uprush of the air through the central
shaft have drained away the most of
he warm air which gave birth to the
notion. the tornado dies away. The
equilibrium of the air-masses is for a
lime restored, the heavier air has fall
en- down upon the surface, and the
warm air. spreading literally as it at
aims the level to which it tends. comes
nto state of quiet Assuming the
width of the destruction brought about
By the storm at six hundred feet, and
he length of its journey at thirty
oiIaS wa find that tho arae ~ ;+s A.